Three weeks ago I had a Baxi Duo-tec Combi 28 HE A boiler installed in my house. Very soon after installation I discovered that in the course of the installation the cold water supply to the tank in the loft had been cut off, which meant that I couldn't get a bath or a shower.

The company sent two guys out who reconnected the supply to the tank but now I can't use the shower (which is gravity fed and attached to the bath mixer tap) because the water comes out either very hot or completely cold and I haven't been able to achieve a steady flow at a comfortable temperature no matter how delicately I've tried to fine tune the hot and cold bath taps which supply the shower head.

It also requires a shower installation that is designed to work with mains pressure water both hot and cold.

Did you have a new shower set up at the same time?

There are two ways round this.

One is to run a cold feed direct to the shower control, simple to do and cheap, the other is, do you have a fitted copper hot water tank?
If you have a hot tank, then join it to the central heating side of the boiler, turn off the direct hot water, and use the system in the traditional way.

A far better solution where there is more than one hot tap, and more than one person who needs hot water at the same time.

The trouble with combi's, is they only work well, when there is high water pressure and only one person using them.

To answer your question: no, I didn't have a new shower set up at the same time. The installer din't give me any reason to think that I needed one, or, indeed, that any modifications to the shower, taps etc were needed.

Also, I did have a fitted hot water tank but this was taken out when the boiler was put in.

Since I've learned that the bath cold tap should be supplied directly from the mains (rather than from the tank in the loft, which is what these guys did when they came back to reconnect a CW supply to my bath/shower) I've phoned the foreman at the firm to tell him that the shower isn't working properly and that I believe that the bath CW should be coming from the mains but he said 'Not necessarily' and that he would speak to the guys who did the job and get back to me. I'm a bit concerned by this response from him - beacuse everything I've read (from you and from one or two other sources) seems to say that the feed does necessarily have to come from the mains.

With all the fuss about saving water, we now have a situation where there are high pressure and low pressure taps and showers. And this is not always obvious from the packaging, one often has to look inside at the specification.

The result is that a tap or shower that worked perfectly at low pressure or high pressure doesn't work properly when connected to the (wrong) supply pressure.

Where you have a shower it really does need the same pressure on both sides. Other mixer taps will work after a fashion.

As far as the bath goes, or any other situation, where there are two separate taps, it should not really be a problem to have low pressure on one and high on the other. You can always run them one at a time.

As your copper tank has gone (I hope they paid you for it) you can either get it back, and set up as before.
Or continue with the new combi supplying mains hot water to all hot taps, and mains cold water to the shower and any mixer taps.

As a matter of interest, why did you change to a combi boiler, when your existing set up was better?

No, they didn't pay me for the copper tank they took away. To be honest I didn't give it much thought! How much would they get for it?

The reason I changed was that my heating stopped working and the guy who came to look at it advised a new system. When he came to look at it he actually got it working by giving the pump a few taps with a hammer but he said it might go again at any time. Also, the back boiler was installed 27 years ago and, although it's only had minimal usage over the years (for various reasons), I thought that now would be an opportune time to change it and save £400 by using the government's current boiler scrappage scheme.

I think my best bet now is to get the company back and put me in a feed from the mains to the bath CW tap.

27 years for a boiler didn't make it old. There are plenty boilers of that age still working perfectly and there are plenty of spares. Modern boilers just don't compare for reliability.
The interesting thing is that the so called efficiency of a boiler is self certified by the manufacturers, there is no system run by anyone to test and compare efficiency. Most of the so called saving is in the short period between start up and reaching operating temperature. Once hot and running there is little to choose between the one you had and the new one.

Basically what you are saying is that the pump, stuck over a period, because it had not been used and instead of taking the cap off and twisting the impeller with a screwdriver as instructed, you bought a new boiler.

One consolation, modern boilers have a system, where as long as you leave them switched on, the control board will run the boiler for a short period every day to ensure the pump doesn't stick.

It can happen to anyone, we cannot all understand and keep up with everything.

Having a combi takes some getting used too.

With an indirect system one lives with a system that is easy.
Your lady can run the tap at the sink slowly with warm water trickling out and wash the vegetables.

With a combi,you turn the tap on, cold water comes out while the boiler does a check then....eventually it lights..... and eventually very hot water comes out, turn it down to a trickle, the boiler turns off......and you have to start again.......more cold water, etc; You lady ends up with sore hands through using cold water.

With a indirect system you can go to any hot tap and hot water comes out, you can have several taps, a shower plus a bath all filling at the same time.

With a combi, you get water from one tap. If someone is having a shower, you dare not turn another tap on, or flush the loo, in case the other person gets burnt or frozen.
If you are on top of a hill, in a low water pressure area, at rush hour times you may have a system that doesn't work at all.

Once again, thanks for your reply, Perry, although it didn't exactly cheer me up to read that I might have been better off repairing my old system! Also, it didn't make me too happy to read of all the combi's shortcomings, although I must say I have become aware of some of them myself, already.

At the moment I'm trying to get the company to come back and change the feed to the bath/shower mixer tap so that it comes from the mains rather than my tank in the loft. Apparently this contravenes water regulations.

I am not sure what you mean, but...
Here is the access point to Building Regs part G
"planningportal.gov.uk/uploads/br/100312_app_doc_G_2010.pdf"

Kindly take a look, the information is provided free by the Government.
The new rules apply now.

Part A - Structure
Part B - Fire safety
Part C - Site preparation and resistance to moisture
Part D - Toxic substances
Part E - Resistance to the passage of sound
Part F - Ventilation
Part G - Hygiene
Part H - Drainage and waste disposal
Part J - Combustion appliances and fuel storage systems
Part K - Protection from falling, collision and impact
Part L - Conservation of fuel and power
Part M - Access to and use of buildings
Part N - Glazing - safety in relation to impact, opening and cleaning
Part P - Electrical safety

They set out the broad objectives or functions which the individual aspects of
the building design and construction should set out to achieve.

They are therefore often referred to as 'functional requirements' and are expressed in
terms of what is 'reasonable', 'adequate', or 'appropriate'.

Thanks for that, Perry, although I couldn't find anything directly relating to my own problem in that link. However, I've had a water board inspector come to my house and he has confirmed that the installation is incorrect and contavenes regs.